Re: [Boost-users] std::vector< boost::shared_ptr<int> >::pop_back()

From: bringiton bringiton (kneeride_at_[hidden])
Date: 2006-07-10 10:00:55

>>just look at the include files:

i looked at the header, but got a little confused.
i don't see how you can call a destruct of a a memory space that still
exists. ie a C version of a vector.

shared_ptr<int> list[1024];
int n = 0;

// add an item
shared_ptr<int> newItem(new int(1));
list[n++] = newItem;

// remove the tail item
n--;
// destructor never called

is it possible to call a destructor of an object that exists?
what then happens then the object goes out of scope? the destructor will be
called twice.

(or maybe i am completely missing the point)

BTW: not sure if above code compiles (did it in my head)

On 7/10/06, Boris Breidenbach <Boris.Breidenbach_at_[hidden]>
wrote:
>
> On Mon, Jul 10, 2006 at 03:58:19PM +1000, bringiton bringiton wrote:
> > This question is based on curiosity. How does std::vector::pop_back()
> call
> > the destructor of the item getting removed?
> >
> > i understood std::vector to be a contigious array of memory, therefore
> an
> > item's memory does not go out of scope when being popped. ie the item
> goes
> > out of scope when the entire array goes out of scope.
>
> just look at the include files:
>
> bits/stl_vector.h says:
> void
>      pop_back()
>      {
>        --this->_M_impl._M_finish;
>        std::_Destroy(this->_M_impl._M_finish);
>      }
>
> so the destructor is called in std::_Destroy.  Which can be found in
> bits/stl_construct.h:
> /**
>   * @if maint
>   * Destroy the object pointed to by a pointer type.
>   * @endif
>   */
> template<typename _Tp>
>    inline void
>    _Destroy(_Tp* __pointer)
>    { __pointer->~_Tp(); }
>
> It just calls the destructor.
>
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